Proguard - Can't find common super class of [com/google/android/gms/d/kl]

Question

I am failing to create a release build. Suddenly Android Studio started throwing below error.

Unexpected error while performing partial evaluation:
  Class       = [com/google/android/gms/d/lc]
  Method      = [a(Lcom/google/android/gms/d/kk;Landroid/content/Context;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lcom/google/android/gms/d/lh;Lcom/google/android/gms/d/en;Lcom/google/android/gms/d/lb;)Lcom/google/android/gms/d/kn;]
  Exception   = [java.lang.IllegalArgumentException] (Can't find common super class of [com/google/android/gms/d/kn] (with 1 known super classes) and [java/lang/String] (with 2 known super classes))
Unexpected error while preverifying:
  Class       = [com/google/android/gms/d/lc]
  Method      = [a(Lcom/google/android/gms/d/kk;Landroid/content/Context;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lcom/google/android/gms/d/lh;Lcom/google/android/gms/d/en;Lcom/google/android/gms/d/lb;)Lcom/google/android/gms/d/kn;]
  Exception   = [java.lang.IllegalArgumentException] (Can't find common super class of [com/google/android/gms/d/kn] (with 1 known super classes) and [java/lang/String] (with 2 known super classes))
Warning: Exception while processing task java.io.IOException: java.lang.IllegalArgumentException: Can't find common super class of [com/google/android/gms/d/kn] (with 1 known super classes) and [java/lang/String] (with 2 known super classes)

Here is my Proguard Configurations

-keep public class com.google.android.gms.* { public *; }
-dontwarn com.google.android.gms.**

-keep class com.facebook.ads.** { *; }

Here is the list of gradle dependencies of my project

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    androidTestImplementation('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    implementation 'com.android.support.constraint:constraint-layout:1.1.0'
    implementation 'com.android.support:design:27.1.1'
    implementation 'com.android.support:appcompat-v7:27.1.1'
    implementation 'com.android.support:cardview-v7:27.1.1'
    implementation 'com.google.firebase:firebase-perf:16.0.0'
    implementation 'com.google.firebase:firebase-config:16.0.0'
    implementation 'com.google.firebase:firebase-core:16.0.0'
    implementation 'com.google.firebase:firebase-messaging:17.0.0'
    implementation 'com.google.android.gms:play-services-analytics:16.0.0'
    implementation 'com.google.android.gms:play-services-drive:15.0.1'
    implementation 'com.google.android.gms:play-services-auth:15.0.1'
    implementation 'com.startapp:inapp-sdk:3.8.4'
    implementation 'com.facebook.android:audience-network-sdk:4.28.2'
    testImplementation 'junit:junit:4.12'
    testImplementation 'org.mockito:mockito-core:2.7.1'
    testImplementation 'org.powermock:powermock-mockito-release-full:1.4.9'   
    implementation('com.crashlytics.sdk.android:crashlytics:2.9.1@aar') {
        transitive = true
    }
}

Note Commenting the Facebook audience network dependency fixes the error. Unfortunately I cannot do it permanently from the project.

Please help me identifying the cause of an issue. Thanks in advance.

Answer 1

Finally I managed to fix the error. As I am not Proguard expert, I may be wrong but this is the workaround I see at the moment.

As I have mentioned in the question, Facebook Audience Network causes the problem with the release build and errors are associated with the GMS Play Service library. According to comment posted by @pedrofsn, Facebook Audience Network uses the Google Play Service Ads library.

I started looking into documentation for the error Can't find common super class of . It says that

A class in one of your program jars or library jars is referring to a class or interface that is missing from the input. The warning lists both the referencing class(es) and the missing referenced class(es). There can be a few reasons, with their own solutions:

As it says the warning lists both the referencing class(es) and the missing referenced class(es), I decided to remove dontwarn just to see the warnings by the Proguard & updated my Proguard Configuration as below

-keep public class com.google.android.gms.* { public *; }

-keep class com.facebook.ads.** { *; }

I managed to see all the warnings by Proguard as the screenshot below.

As we can see from the screenshot, google ads library classes cannot find their referenced class com.google.android.gms.common.internal.zzac . My guess is that this class com.google.android.gms.common.internal.zzac should belong to the internal jar of the google ads dependency & that internal jar is probably missing.

So I have manually added the google ads dependency to my app level build.gradle as below

implementation 'com.google.android.gms:play-services-ads:15.0.1' 

And I see I can compile the release build successfully.

Answer 2

我将'com.google.firebase：firebase-messaging：17.0.0'降级为'com.google.firebase：firebase-messaging：15.0.2'

Answer 3

For this to work, I had to uncomment:

buildTypes {
    release {
        //minifyEnabled true
        //shrinkResources true
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}

and add the below to your proguard-rules.pro file:

-keep class com.google.android.gms.internal.** { *; }
-keep public class com.google.android.gms.* { public *; }
-dontwarn com.google.android.gms.**

although uncommenting minifyEnabled is not recommended since it removes dead/unused code